1. Field of the Invention
The present invention relates to a reconfiguration device for a set of W memory units associated with k replacement units or redundant units.
2. Discussion of the Related Art
The applicant has described in patent application PCT/FR02/00523 devices for automatic rerouting between access terminals and fault-free blocks (or units), that is, the faulty memory blocks are replaced with other blocks selected, according to cases, among the neighbors of the faulty block (case of FIG. 1A) or directly among redundant blocks (case of FIG. 1B). In practice, these will be memory blocks, each of which provides a data bit of a 16-, 32- or 64-bit word. In the case of a memory with 32-bit words, 8 redundant blocks will for example have to be added.
FIG. 1A illustrates in a very simplified manner a memory having words of N (four) bits. Each of the bits of the different memory words is stored in a unit of 2m cells (where m is the number of address bits of each memory unit). There thus are W (four) base units of memory cells U0 to U3 and k (three) replacement units U4 to U6. In this example, the number of address bits of each unit is equal to the number of address bits of the memory and W=N, since the unit of the memory considered herein corresponds to the block which comprises all the cells generating a data bit. To perform a replacement, instead of connecting the data input/output terminals d0, d1, d2, d3 directly to memory units U0, U1, U2, U3, it is provided to connect these terminals to the memory units via multiplexers MUX0, MUX1, MUX2, MUX3, respectively controlled by the outputs of a logic reconfiguration circuit RFL associated with W+k=N+k flip-flops F0 to FN+k−1 (F0 to F6) in which, during a previous test phase, the right or erroneous state of the corresponding unit has been indicated. In the case where there are k replacement units, each multiplexer will have k+1 outputs. It should be noted that this multiplexer must be bidirectional to be able to connect the data terminals to the memory blocks during the reading and the writing, or else two multiplexers will be used, one for the reading and one for the writing.
In the embodiment of FIG. 1A, it is provided to replace each faulty memory block with its closest fault-free memory block. A “close” substitution is performed. Each multiplexer is capable of being connected to the unit of same rank and to the three units of immediately greater rank.
In the embodiment of FIG. 1B, any erroneous unit is replaced, not with one of its non-erroneous neighbors, but with one of the replacement units. A “distant” substitution is performed. Each multiplexer comprises an output to the corresponding unit and three outputs to units U4 to U6.
To determine to which unit the rerouting must be performed, account must be taken of the state of the already examined units, for example, those located to the right (or to the left) of a considered unit, and of the state of the possible replacement units. Patent application PCT/FR02/00523 describes various means for automatically performing this rerouting once the erroneous units have been identified by the testing.
FIG. 2 illustrates in a logic and simplified manner the system of FIGS. 1A and 1B. The inputs/outputs of a memory comprising W+k=N+k units (U0 to UN+k−1) are associated with W=N multiplexers of 1 from among k+1 (MUX0 to MUXN−1) connected to N input/output terminals (I/O). Each multiplexer receives k+1 control signals from a logic reconfiguration circuit RFL coupled to W+k=N+k defect location storage cells FLSC0 to FLSCN+k−1.
The repair process described hereabove may be called a static process. A memory being divided into a number of blocks, each of which provides one data bit, a number of redundant blocks intended to replace erroneous memory blocks is provided. Once the memory and the replacement blocks have been tested, the reconfiguration of the outputs between the base blocks (or regular blocks) and the replacement blocks is definitively performed (or programmed). In a memory with 32-bit words, to repair 8 faults distributed in 8 blocks, 8 redundant blocks must be provided. Then, the surface area taken up by the replacement blocks is equal to one quarter of the surface area of the base blocks.